4,8-dicyclohexyl-6-hydroxy-2,10-dimethyl-12H-dibenzo[d,g][1,3,2]dioxaphosphocin

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:

toxicity to aquatic algae and cyanobacteria

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
According to REACH Annex VII column 1, 9.1.2. Growth inhibition study aquatic plants (algae preferred) shall be conducted. According to column 2, 9.1.2. The study does not need to be conducted if there are mitigating factors indicating that aquatic toxicity is unlikely to occur for instance if the substance is highly insoluble in water or the substance is unlikely to cross biological membranes.
In general, there is no legal limit value available defining a substance as poorly water soluble or insoluble under REACH. However, in ECHA’s Guidance document Chapter R.7b: Endpoint specific guidance Version 3.0 – February 2016, it is stated: „poorly water soluble substances (e.g. water solubility below 1 mg/L or below the detection limit of the analytical method of the test substance)“. Further, poorly soluble substances are defined by OECD (2000 OECD SERIES ON TESTING AND ASSESSMENT, Number 23, GUIDANCE DOCUMENT ON AQUATIC TOXICITY TESTING OF DIFFICULT SUBSTANCES AND MIXTURES, ENV/JM/MONO(2000)6) as substances with a limit of solubility <100 mg/l although technical problems are more likely to occur at <1mg/l as defined in TGD (1996). Very low water solubility (i.e. in the low μg/l range) could be used as a reason to significantly modify a standard test or to test non-pelagic organisms preferentially.
ECHA’s Guidance document Chapter R.7c: Endpoint specific guidance Version 3.0 – June 2017 further says: „As indicated in the OECD TG 305, for strongly hydrophobic substances (log Kow > 5 and a water solubility below ~ 0.01-0.1 mg/L), testing via aqueous exposure may become increasingly difficult. However, an aqueous exposure test is preferred for substances that have a high log Kow but still appreciable water solubility with respect to the sensitivity of available analytical techniques, and for which the maintenance of the aqueous concentration as well as the analysis of these concentrations do not pose any constraints.

The registrant did conduct or had conducted various studies ahead, as a part of a tiered approach, to establish suitable conditions including analytics for water solubility and hydrolysis testing. Details can be found in the respective chapters, summarizing however it can be stated the following:
NMR spectra done with other solvents than water indicate decay of the test item into raw material and phosphonic acid in the presence of water, no suitable solvent system for monitoring in-situ hydrolysis in water was found. Water solubility determinations show, that 4,8-dicyclohexyl-6-hydroxy-2,10-dimethyl-12H-dibenzo[d,g][1,3,2]dioxaphosphocin degrades in water over time into raw material. Both substances are insoluble in water, the besides that formed phosphonic acid is soluble in water and lowers the pH-value of the solution.
The solubility of the test item in water was estimated to be 1.171*10-8 mg/L at 25 °C (EPI Suite 4.11). A study to investigate the hydrolytic properties of 4,8-dicyclohexyl-6-hydroxy-2,10-dimethyl-12H-dibenzo[d,g][1,3,2]dioxaphosphocin can not be performed, because no analytical method with appropriate sensitivity is available or could be developed.
In consequence, both water solubility and hydrolysis study according to OECD 105 resp. 111 cannot be performed, and testing is technically not feasible.

Based on the available information it can be stated that, as outlined in the first waiving possibility under REACH, the substance is highly insoluble in water, and hence, aquatic toxicity is unlikely to occur. The latter conclusion is supported by available studies conducted prior to REACH implementation, i.e. each a study according to EU method C.1 and EU method C.11. In those studies, no effects were noted in concentration of 1 mg/l (C.1) resp. 10 g/l (C.11), which are way above the possible water solubility of the registered substance. Hence, a study of the toxicity of the registered substance against algae does not need to be conducted. With a estimated water solubility of 1.171*10-8 mg/L the substance does not only need to be regarded as poorly soluble but practically insoluble in water, as very low water solubility can be assumed if the substance is soluble only in the low μg/l range, and the actual water solubility is way below. Further, the registrant demonstrated that the analysis of concentrations in water poses constraints, the sensitivity of available analytical techniques is not sufficient to analyse concentrations in the estimated water solubility range of 1E-8 mg/l.

In consequence, testing can be omitted.